1. Field of the Invention
The invention relates to an apparatus for controlling a hybrid vehicle having an internal combustion engine and a motor (electric motor) as driving sources for the vehicle.
2. Description of the Related Background Art
A hybrid vehicle having an engine and a motor as driving sources has conventionally been well known. For example, a control apparatus for the hybrid vehicle is shown in JP-A-3-121928.
In the control apparatus, the motor is driven and an output of the engine is controlled in accordance with a driving state of the vehicle. Specifically, an operating mode of the motor is discriminated in accordance with the driving state of the vehicle, in an accelerating mode, a driving electric power is supplied to the motor and the output of the engine is assisted, and in a decelerating mode, the motor is set into a regeneration braking state and a regeneration electric power by the motor is charged into a battery. The electric power charged in the battery is used as a motor driving electric power in the accelerating mode.
Even in the hybrid vehicle, an air-fuel ratio of an air-fuel mixture which is supplied to the engine is controlled in accordance with the driving state of the vehicle. For instance, when the driving state indicates a cruising driving, a target air-fuel ratio is set to a lean air-fuel ratio (for example, 16) for the purpose of improvement of mileage and a lean burn control is performed. In a driving state where an engine output is needed, the target air-fuel ratio is set to a stoichiometric air-fuel ratio (for example, 14.7) and a stoichiometric burn control is performed. In the lean burn control, since an output torque of the engine decreases as compared with that in the stoichiometric burn control, a difference of the output torque of the engine is large at the time of driving in the case where the control suddenly changes from the lean burn control to the stoichiometric burn control or from the stoichiometric burn control to the lean burn control. When this occurs, a torque shock results.
It is well known that an electronic throttle valve control apparatus to control an opening degree of a throttle valve of an internal combustion engine is used to reduce the torque shock. According to the electronic throttle valve control apparatus, ordinarily, when a driver operates an acceleration pedal, the opening degree of the throttle valve is controlled so that the driver can obtain a proper speed sense in correspondence to the operation of the acceleration pedal. At the time of the sudden change of the air-fuel ratio as mentioned above, the electronic throttle valve control apparatus controls the opening degree of the throttle valve irrespective of the operation of the acceleration pedal and operates so that the output torque of the engine does not suddenly change. There is also a case where a secondary air supplying apparatus for supplying secondary air into an intake pipe arranged on the downstream of the throttle valve is used to similarly reduce the torque shock.
Even if the electronic throttle valve control apparatus or secondary air supplying apparatus operates in order to prevent the change in output torque of the engine when the air-fuel ratio suddenly changes, however, there is a problem that the output torque difference cannot be sufficiently compensated so as not to cause a torque shock because of a time delay which is caused until a control result is reflected due to a delay of the air supply to the engine.
It is, therefore, an object of the present invention to provide a control apparatus of a hybrid vehicle which can sufficiently compensate an output torque difference of an engine at the time of sudden change of an air-fuel ratio of a supply air-fuel mixture without a time delay.
According to the present invention, there is provided a control apparatus of a hybrid vehicle having an internal combustion engine and an electric motor as driving sources for the vehicle, the electric motor operating as a motor to assist an output of the internal combustion engine and operating as a generator to regenerate running energy of the vehicle and to charge voltage storage means. The apparatus comprises: air-fuel ratio detecting means for detecting a change in air-fuel ratio of an air-fuel mixture which is supplied to the engine; and electric motor control means for making the electric motor operative as a motor when it is detected by the air-fuel ratio detecting means that the air-fuel ratio has changed from a rich side value to a lean side value, and for making the electric motor operative as a generator when it is detected that the air-fuel ratio changed from the lean side value to the rich side value.
According to the control apparatus of a hybrid vehicle of the invention, for example, when it is detected that the air-fuel ratio of the supply air-fuel mixture to the engine changed to the lean side value because the control is changed from the stoichiometric burn control to the lean burn control, the electric motor is made operative as a motor in order to assist the output of the engine immediately after that, and for instance, when it is detected that the air-fuel ratio of the supply air-fuel mixture changed to the rich side value because the control is changed from the lean burn control to the stoichiometric burn control, the electric motor is made operative as a generator for the purpose of regeneration braking immediately after that. The output torque difference of the engine, therefore, at the time of the change in air-fuel ratio of the supply air-fuel mixture can be sufficiently compensated without a time delay.
In the control apparatus of a hybrid vehicle of the invention, the output torque difference of the internal combustion engine when the change in the air-fuel ratio is detected is presumed in accordance with the driving state of the vehicle, and one of a driving force and a regeneration braking force of the electric motor is controlled in accordance with the presumed output torque difference, so that a proper driving state or regenerating state of the motor can be obtained for the output torque difference of the engine at the time of the change in air-fuel ratio of the supply air-fuel mixture.
Further, in the control apparatus of a hybrid vehicle of the invention, when it is detected by the air-fuel ratio detecting means that the air-fuel ratio has changed to the lean side value, the electric motor is made operative as a motor and, after that, the driving force of the motor is gradually decreased, and when it is detected by the air-fuel ratio detecting means that the air-fuel ratio has changed to the rich side value, the electric motor is made operative as a generator and, after that, the regeneration braking force of the generator is gradually reduced, so that the force can be made coincide with the proper output torque after the sudden change of the air-fuel ratio without causing a torque shock.